A continuous commercial power supply-type uninterruptible power supply device includes a switch having a first terminal for receiving alternating current (AC) power from a commercial AC power supply and a second terminal connected to a load, and a power converter connected to the load. When an AC voltage from the commercial AC power supply is normal, the switch is set to an ON state, and the AC power from the commercial AC power supply is supplied to the load via the switch. When the AC voltage from the commercial AC power supply becomes abnormal, the switch is set to an OFF state, and direct current (DC) power supplied from a DC power supply is converted into AC power by the power converter and supplied to the load.
Japanese Patent Laying-Open No. 11-341686 (PTD 1) and Japanese Patent Laying-Open No. 2003-333753 (PTD 2) disclose a technique in which a switch without having self arc extinguishing capability is used, and, when an AC voltage from a commercial AC power supply becomes abnormal, an output current of a power converter is controlled to reduce a current flowing into the switch and quickly extinguish an arc in the switch.